An efficient optimal reconfiguration algorithm for FDDI-basednetworks

We study a new network architecture based on standard FDDI networks. This network, called FDDI-based reconfigurable network (FBRN), is constructed using multiple FDDI token rings and has the ability to reconfigure itself in the event of extensive damage to the network. Thus, an FBRN has the potential to provide high available bandwidth even in the presence of numerous faults. Realization of this potential depends crucially on a reconfiguration algorithm that guides the reconfiguration process. We design and analyze a reconfiguration algorithm for FBRNs. Our algorithm is optimal in the sense that it always produces a configuration that results in the maximum available bandwidth for a given fault pattern. This algorithm has a polynomial time complexity. We also show that the available bandwidth of an FBRN is dramatically improved with our reconfiguration algorithm     

Cycle Time Properties Of The FDDI Token Ring Protocol

The FDDI Token Ring Protocol controls communication over fiber optic rings with transmission rates in the range of 100 megabits per second. It is intended to give guaranteed response to time-critical messages by using a "timed token" protocol, in which non-critical messages may be transmitted only if recent movement of the token among stations has been sufficiently fast relative to a "target" token rotation time (TTRT).     

A performance analysis of an object-based I/O architecture in a video server environment

In this paper, we present a performance analysis of how effective video server applications can be supported on personal computers (PCs) connected through a local area network (LAN). We considered both the standard 16-Mbit/s token ring and a 100-Mbit/s token ring, which follows closely the specifications for the Fiber Distributed Data Interface (FDDI). We examined three I/O architectures for a PC-based video server: an interrupt-driven I/O architecture, a peer-to-peer I/O architecture, and a concurrent, object-based I/O architecture that we proposed. The video server must support multiple MPEG-1 video streams at the same time to multiple clients on the LAN. We found that the network protocol layers require a lot of processing power, and that an implementation of our proposed I/O architecture, which takes advantage of the available power of the host processor to off-load I/O adapters, can deliver much better performance, and is more cost-effective, than other I/O architectures in a video server environment.     

Synchronous bandwidth allocation in FDDI networks

It is well known that an FDDI token ring network provides a guaranteed throughput for synchronous messages and a bounded medium access delay for each node/station. However, this fact alone cannot effectively support many real-time applications that require the timely delivery of each critical message. The reason for this is that the FDDI guarantees a medium access delay bound to nodes, but not to messages themselves. The message-delivery delays may exceed the medium-access delay bound even if a node transmits synchronous messages at a rate not greater than the guaranteed throughput. We solve this problem by developing a synchronous bandwidth allocation (SEA) scheme which calculates the synchronous bandwidth necessary for each application to satisfy its message-delivery delay requirement. The result obtained in this paper is essential for effective use of the FDDI token ring networks in supporting such real-time communication as digital video/audio transmissions, and distributed control/monitoring     

Hard Real-Time Communication with the Timed Token Protocol: Current State and Challenging Problems

With the increasing use of distributed real-time systems, the ability of communication networks to handle real-time traffic is becoming more and more important. The timed token medium access control protocol, which has been now incorporated into several network standards such as FDDI and SAFENET due to its special timing property of bounded medium access time, is one of the most suitable and attractive candidate communication protocols for supporting distributed hard real-time applications. Extensive research has been conducted on using the timed token protocol to guarantee timely transmission of messages in a communication environment with hard real-time requirements. This paper intends to present a comprehensive review on recent advances in hard real-time communication with the timed token protocol. In addition, several challenging problems are identified.     

分布式系统临界区的时控令牌访问算法及其排队模型

文章结合在分布式光纤数据接口FDDI中应用的时控令牌协议,对现有分布式系统临界区互斥访问的令牌环算法进行了改造。并对改进后的系统模型进行了分析,建立了相应的排队模型,并对一种简化模型L／D／1／1／FCFS（相关）进行了解析和模拟实验。模拟实验结果显示时控令牌协议下的系统稳定状态是两个稳定状态交替出现形成的。     

Reliability mechanisms of the FDDI high bandwidth token ring protocol

The Fiber Distributed Data Interface (FDDI) is an ANSI draft proposed standard for a 100 megabit per second token ring using fiber optics as the transmission medium. The FDDI design represents an extensive effort to incorporate reliability mechanisms as an integral part of the design. These mechanisms provide fault detection and isolation functions, monitoring functions, and configuration functions. The purpose of this paper is to discuss these reliability mechanisms, and to compare and contrast them with reliability mechanisms which have been incorporated in other local area network architectures.     

Fast gossiping in square meshes/tori with bounded-size packets

Gossiping is a communication problem in which each node has a unique message (token) to be transmitted to every other node. The nodes exchange their tokens by means of packets. A solution to the problem is judged by how many rounds of packet sending are required. In this paper, we consider a version of the problem in which small-sized packets (each carrying exactly one token) are used, the links (edges) of the network are half-duplex (only one packet can flow through a link at a time), and the nodes are all-port (a node's incident edges can all be active at the same time). This is also known as the H* model. We study the model on a 2D square mesh and on a 2D square torus. An improved, asymptotically optimal algorithm for the mesh and an optimal algorithm for the torus are presented     

Providing per-session deterministic quality of service guarantees in cross-path packet switch

Recently, a quasi-static routing scheme called path switching was proposed for large-scale packet switch systems. The path-switched Clos network is called a cross-path switch. Cross-path switch is capable of supporting multirate and multicast traffic. In this paper, we develop a general framework for it to handle multimedia traffic. We obtain upper bounds on the delay and backlog at the cross-path switch on a per-session basis, wherein no packet lost or delay bound violation is allowed. Our results show that these bounds much depend on the way of token assignment at the central stage. To understand such dependence, we quantify the effect of the token assignment on the switch performance. From these results, we design an effective token assignment scheme to achieve better performance guarantees in the switch. We show that cross-path switch with such token assignments always provides near-optimal performance guarantees to each data session.     

Token bucket characterization of long-range dependent traffic

The token bucket characterization provides a deterministic yet concise representation of a traffic source. In this paper, we study the impact of the long-range dependence (LRD) property of traffic generated by today's multimedia applications on the optimal dimensioning of token bucket parameters. To this aim, we empirically illustrate the difference between the token bucket characteristics of traffic exhibiting different degrees of time dependence but with identical macroscopic properties (i.e. inter-arrival time and packet size distributions). In addition, we use a statistical model to analytically determine optimal token bucket parameters under various optimization criteria. The statistical model is based on fractional Brownian motion and takes LRD into account. We apply this model to several aggregated MPEG video sources. We then assess the validity of these analytic results by comparing them to empirical results. We conclude that the analytic approach presented here is effective in optimally sizing token buckets for LRD traffic, and promises to be applicable under different traffic conditions and for various optimization criteria.     

Profibus-DP网络的FDL时态特性分析

介绍了非立即无数量约束低优先级报文传送模式在持有令牌时闻内的处理流程．基于报文周期时间对Profibus-DP的时态特性进行分析,讨论了不同数据传输率下的标准周期和非周期报文对标准周期的影响,进一步确定了目标令牌循环时间的下界,并给出了设置方法．     

基于双子代数理论的网络建模与分析

本文研究了双子代数尤其是极大代数理论在计算机网络建模与性能分析中的应用。采用极大代数分析了令牌桶的输入输出特性,得到了(b,ρ)令牌桶在极大代数下的状态空间方程组与传输矩阵;提出了基于极大代数的网络演算,定义了极大到达曲线与极大服务曲线,利用这两个概念得出了极大代数下有关延迟以及输出流突发性的定理。最后采用基于极大代数的网络演算对非抢占优先级多路复用以及保证速率服务器两个模型进行了分析,得出了两种模型各自在极大代数网络演算下的服务曲线。本文还把基于极大代数的网络分析方法与基于极小代数的分析方法进行了比较,阐明了基于极大代数方法的优点与适用场合。     

Conventional and early token release scheduling models for the IEEE 802.5 token ring

We develop analyticalscheduling models for both the original IEEE 802.5 token ring protocol and a recent extension to the original protocol that allows early token release (ETR). A scheduling model is an abstraction that supports reasoning about the timing correctness of a given set of real-time messages scheduled on the network. Scheduling analysis of the original IEEE 802.5 token ring protocol has previously been discussed in Strosnider and Marchok (1989) and Pleinevaux (1992) in the context of improving responsiveness of soft deadline aperiodic messages. In contrast, this paper develops schedulability conditions for arbitrary periodic message sets. The main contributions of this work are: Scheduling models for both the original protocol and ETR protocol; comparison for maximum achievable utilizations for the two protocols; comparison between the original protocol and ETR from a schedulability viewpoint. We also demonstrate the utility of our scheduling models to select network operating parameters such as maximum packet size, and to quantify effects of parameters such as the number of stations, and network size on schedulability.     

噪音环境下的FF Fieldbus通讯性能研究

通过噪音对令牌运行过程的作用,本文分析了在噪音环境下FF Fieldbus的性能变化 ．本文首先建立了令牌运行过程的自动机模型,然后利用此模型分析了噪音对令牌运行方式 的影响．根据噪音的影响,本文推导出令牌运行时间和令牌平均运行时间．最后利用解析表 达式分析出噪音分布对FF Fieldbus性能的影响．     

Determination of path identifiers for reliability analysis of a broadcasting network using Petri nets

A Petri net approach for determination of the sets of path identifiers for reliability analysis of a broadcasting network is presented. The firing concept of Petri nets is exploited to give a Petri net interpretation to certain properties of the network. The dynamic behaviour of the system under study is represented in the form of token movements within the model. The various entities of Petri nets are assigned an appropriate interpretation for studying the behaviour of the system at different levels. Corresponding to the source node and each of the terminal nodes, a vector, representing the state of the Petri net interpreted model, is defined by assuming a token initially at the source place and finally at one of the terminal places. The reachability and marking concepts are then used to determine all success states of the system. The developed algorithm has been coded into FORTRAN-77 and the complete package is available. The proposed technique is extremely simple as it uses only vector additions on the columns of the place-to-transition incident matrix.     

Self-stabilizing depth-first token circulation in arbitrary rooted networks

Abstract. We present a deterministic distributed depth-first token passing protocol on a rooted network. This protocol uses neither the processor identifiers nor the size of the network, but assumes the existence of a distinguished processor, called the root of the network. The protocol is self-stabilizing, meaning that starting from an arbitrary state (in response to an arbitrary perturbation modifying the memory state), it is guaranteed to reach a state with no more than one token in the network. Our protocol implements a strictly fair token circulation scheme. The proposed protocol has extremely small state requirement – only states per processor, i.e., bits per processor, where is the degree of the network. The protocol can be used to implement a strictly fair distributed mutual exclusion in any rooted network. This protocol can also be used to construct a DFS spanning tree. Received: July 1998 / Accepted: April 2000     

基于拟生灭过程的多跳Ad hoc网络洪泛方式下拥塞控制及饱和条件研究

802.11Ad hoc网络中拥塞控制是保证网络稳定性的重要因素。拥塞发生时,通常的做法是控制流量,而研究网络何时出现拥塞则是目前的首先任务。针对多跳Ad hoc网络,对单个节点的数据发送过程,考虑包的最大重传次数、数据包的缓冲队列,提出一种新的基于802.11MAC接入协议DCF Basic Access机制的无限状态拟生灭过程模型。研究了在洪泛方式下为避免网络到达饱和状态,节点MAC层上数据包的到达率应满足的条件。指出在DCF协议下到达率对网络状态的影响。与现有文献的区别是,从网络层的角度进行研究,提出了一种新的更精确地描述数据发送过程的模型。给出了多跳Ad hoc网络中稳定性与数据到达率的数学关系式,为多跳Ad hoc网络的拥塞控制提供了一个重要的参考。     

The timed-token protocol for real-time communications

The timed-token protocol is a token-passing protocol in which each node receives a guaranteed share of the network bandwidth. Partly because of this property, the timed-token protocol has been incorporated into a number of network standards, including the IEEE 802.4 token bus, the Fiber Distributed Data Interface (FDDI), and the Survivable Adaptable Fiber Optic Embedded Network (Safenet). Networks based on these standards are becoming increasingly popular in new generation real-time systems. In particular, the IEEE 802.4 standard is included in the Manufacturing Automation Protocol (MAP), which has been widely used in computer-integrated manufacturing and industrial applications. Meeting message deadlines requires proper control of medium access. In the timed-token protocol, access to the communication medium is controlled by a token that is passed among the nodes in a circular fashion. Messages are segregated into two separate classes: synchronous and asynchronous. Synchronous messages, used for real-time communication, can have deadline constraints and thus are given a guaranteed share of the network bandwidth. The authors focus on meeting the deadlines of synchronous messages     

Self-organizing continuous attractor networks and path integration: one-dimensional models of head direction cells

Some neurons encode information about the orientation or position of an animal, and can maintain their response properties in the absence of visual input. Examples include head direction cells in rats and primates, place cells in rats and spatial view cells in primates. 'Continuous attractor' neural networks model these continuous physical spaces by using recurrent collateral connections between the neurons which reflect the distance between the neurons in the state space (e.g. head direction space) of the animal. These networks maintain a localized packet of neuronal activity representing the current state of the animal. We show how the synaptic connections in a one-dimensional continuous attractor network (of for example head direction cells) could be self-organized by associative learning. We also show how the activity packet could be moved from one location to another by idiothetic (self-motion) inputs, for example vestibular or proprioceptive, and how the synaptic connections could self-organize to implement this. The models described use 'trace' associative synaptic learning rules that utilize a form of temporal average of recent cell activity to associate the firing of rotation cells with the recent change in the representation of the head direction in the continuous attractor. We also show how a nonlinear neuronal activation function that could be implemented by NMDA receptors could contribute to the stability of the activity packet that represents the current state of the animal.     

令牌多环网性能—可靠性综合评价

网络的性能与可靠性已分别得到广泛的研究,然而,怎样分析具有容错机制的环网的性能仍属有待开拓的研究领域,本文提出了一种分析具有自修复机制的多环网络系统的方法,并给出了报文传输时间分布的拉氏变换式,平均等待时间及平均队列长度公式,分析结果可用于评估故障与修复过程对实时令牌环网的实时响应特性的影响,对基于LAN的分布式实时系统设计具有指导意义。